Vascular occlusions restrict the flow of blood to tissue and organs can cause a variety of problems. For example, occlusions that restrict blood flow to the heart can cause heart attacks and angina, and occlusions that restrict blood flow in cerebral blood vessels (e.g., cerebral arteries and veins) can cause strokes and other neurological problems. It is therefore desirable that these occlusions be opened up and removed.
A minimally invasive method of recanalizing an occlusion involves ablating, cutting, pulverizing, dissolving, or otherwise penetrating the occlusion with a vascular catheter. When the catheter reaches the occlusion, a device at the catheter's distal tip is advanced into the occlusion where it performs the operation to cross or penetrate the occlusion. The catheter may also include components that capture, suction or otherwise prevent the occlusion fragments from traveling downstream and creating another blockage.
Advancing the catheter to the site of the occlusion is generally done with the aid of a guidewire that has a smaller distal profile than the catheter itself. Guidewire tips are also designed to be relatively small and stiff so that then can more easily penetrate and advance through the occlusion, providing a path or rail for the subsequently advancing catheter to follow through the occlusion. This process is relatively simple for treating acute occlusions made of relatively soft tissue and occlusions that do not completely block the passage of blood and other fluids through the vessel.
However, another class of occlusions known as chronic total occlusions (CTOs) has been treated less successfully with intravascular catheter procedures. CTOs are generally calcified, fibrotic occlusions that are difficult to penetrate with conventional guidewires. Compounding the problem is that CTOs typically create a complete blockage of the vessel, making it difficult or impossible to flow angiographic contrast agent around the occlusion. This prevents a treating physician from using fluoroscopy, for example, to see a guidewire being advanced into and through the occlusion. Without proper navigation tools there is a significant possibility that the physician may perforate the blood vessel while advancing the guidewire.
The difficult to penetrate nature of CTOs, and the fact that they oftentimes prevent the flow of contrast agent through a vessel have made this class of vascular occlusions difficult to treat with conventional vascular catheters. Successful treatment of CTOs with these devices or methods currently runs about 50 and 60%, with a high risk of blood vessel perforation. Thus, there is a need for new catheter designs and treatment procedures that increase the success rate for successful crossing and recanalization of CTOs.